This paper proposes a model of a legislature, formed by several parties, which
have to vote for or against a certain bill in the presence of a lobbyist who is interested
in a certain outcome of the vote. We show that the ease of manipulating a legislature
decision by the lobbyist is increasing with the number of parties. A high threshold
leads to fewer parties represented, and consequently, decreases the ease of changing
a legislature decision by the lobbyist. On the other hand, a high threshold may
cause a misrepresentation of voters. We show that if the threshold is higher that
6%, the impact of the misrepresentation effect becomes significant.